Unless you directly shock yourself in the process, you should not get a shock by simply touching the person getting shocked. To get shocked, you would have to complete the circuit by placing yourself in the middle of the current. In the use of the Taser, touching the person between the attached probes will give you a good dose. For this reason, police are trained to wait until the instant the shock stops, to go in for physical control and cuffing. The danger of touching the wires or getting in between the probes while the person is locking up an twitching is a very real possibility. If two people are fighting on the ground and one is hit with a Taser, the circuit will not be complete to shock both unless the other guy is connected between the probes or one of the probes is connected to him.
Most commercially available pepper sprays will retain their consistency and mixture through the agitation of normal carry on your person. Unless you keep it on a shelf for a long period of time, just the movement of walking around and getting in and out of a car should be enough to keep the cannister and contents functional.